ZnO Nanowires Research Articles

Effect of nanoscale interface modification on residual stress evolution during composite processing

The interface characteristics of the matrix and fibers significantly influence the evolution of residual stress in composite materials. In this study, we provide a methodology for reducing the residual stress in laminated composites by modifying the thermomechanical properties at the fiber–matrix interface. A hydrothermal chemical growth method was used to grow Zinc Oxide nanowires on the carbon fibers. We then utilized a novel digital image correlation approach to evaluate strains and residual stresses, in situ, throughout the autoclave curing of composites. We find that interface modification results in the reduction of residual stress and an increase in laminate strength and stiffness. Upon growing ZnO NWs on the carbon fibers, the maximum in situ in-plane strain components were reduced by approximately 55% and 31%, respectively, while the corresponding maximum residual stresses were decreased by 50.8% and 49.33% for the cross-play laminate [0°/90°] layup in the x and y directions, respectively. For the [45°/-45°] angle ply layup in the x-direction, the strain was decreased by 27.3%, and the maximum residual stress was reduced by 41.5%, whereas in the y-direction, the strain was decreased by 166.3%, and the maximum residual stress was reduced by 17.8%. Furthermore, mechanical testing revealed that the tensile strength for the [45°/-45°] and [0°/90°] laminates increased by 130% and 20%, respectively, with the interface modification.

Sacrificial Doping as an Approach to Controlling the Energy Properties of Adsorption Sites in Gas-Sensitive ZnO Nanowires

Currently, devices for environmental gas analyses are required in many areas of application. Among such devices, semiconductor-resistive gas sensors differ advantageously. However, their characteristics need further improvement. The development of methods for controlling the surface properties of nanostructured metal oxides for their use as gas sensors is of great interest. In this paper, a method involving the sacrificial doping of ZnO nanowires to control the content of their surface defects (oxygen vacancies) was proposed. Zinc oxide nanowires were synthesized using the hydrothermal method with sodium iodide or bromide as an additional precursor. The surface composition was studied using X-ray photoelectron spectroscopy. The sensor properties of the isopropyl alcohol vapors at 150 °C were studied. It was shown that a higher concentration of oxygen vacancies/hydroxyl groups was observed on the surfaces of the samples synthesized with the addition of iodine and bromine precursors compared to the pure zinc oxide nanowires. It was also found out that these samples were more sensitive to isopropyl alcohol vapors. A model was proposed to explain the appearance of additional oxygen vacancies in the subsurface layer of the zinc oxide nanowires when sodium iodide or sodium bromide was added to the initial solution. The roles of oxygen vacancies and surface hydroxyl groups in providing the samples with an increased sensitivity were explained. Thus, a method involving the sacrificial doping of zinc oxide nanowires has been developed, which led to an improvement in their gas sensor characteristics due to an increase in the concentration of oxygen vacancies on their surface. The results are promising for percolation gas sensors equipped with additional water vapor traps that work stably in a high humidity.

Decoupling Acoustoelectric and Thermal Effects of Ultraviolet Responses for Acoustic Wave Sensing Mechanisms

Ultraviolet (UV) detectors based on surface acoustic wave (SAW) technology offer unique advantages of remote or wireless operation capability with a potential of zero power consumption. Frequency shift of SAW devices induced by UV irradiation is mainly caused by acoustoelectric and thermal effects, although mass-loading and photo-capacitive effect might also have minor influences. Currently the individual contribution from either acoustoelectric effect or thermal effect for UV sensing has not been thoroughly studied. In this work, we systematically investigated the contribution of acoustoelectric and thermal effects at different UV light intensities based on a LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SAW device with its wavelength of 20 μm, and decoupled their individual contributions to the overall ultraviolet responses for acoustic wave sensing. We found that for the LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SAW device without any surface treatment, the frequency shift was mainly caused by the thermal accumulation induced by UV radiation. Whereas for the LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SAW devices coated with zinc oxide nanowires (ZnO NWs), the frequency shift is caused by the combined acoustoelectric and thermal effects. We found that the frequency shift caused by acoustic electric effect is dominant at a low UV intensity (< 30 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). Whereas with the UV light intensity larger than 90 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the photogenerated carriers generated by ZnO NWs became saturated, and then the thermal effect became dominant. This study clarifies the nature of individual influences of these two factors on the dominant mechanisms of the SAW based UV sensing at different conditions.

Transparent Flat Panel X-Ray Source Using ITO Transmission Anode and ZnO Nanowire Cold Cathode

X-ray sources have important applications in medical diagnosis, industrial inspection, etc. Transparent X-ray source has not been reported before, which enables the applications such as simultaneous imaging using X-ray and visible light. In this article, a fully vacuum-encapsulated transparent flat-panel X-ray source was prepared by using ZnO nanowires cold cathode and indium-tin-oxide (ITO) transmission anode. The effect of thicknesses of ITO film on X-ray radiation intensity was studied. A radiation dose rate of 6.85 mGy/s measured at 5 cm in front of the flat-panel X-ray source (FPXS) under 48-kV anode voltage and an optical transmittance of 72.63% at 550-nm light were achieved. X-ray spectra show the indium is the main element to generate the X-ray. By adopting the device in an X-ray and visible light dual-functional inspection set-up, the X-ray and visible light imaging of objects were demonstrated simultaneously.

From UV to Vis Broadband Photodetectors Based on ZnO/CuO/NiO Core–Shell–Shell Heterojunction Nanostructures

In recent years, with the development of wearable electronics, the demands for high-performance photodetectors with smaller size, lower power consumption, and higher sensitivity have increased remarkably. Photodetectors based on one-dimensional (1D) zinc oxide (ZnO) nanowires (NWs) have been intensively investigated owing to their geometrical nanostructure possessing a large surface-to-volume ratio, high carrier mobility, and adjustable optical absorption. However, ZnO NW photodetectors usually can only detect ultraviolet (UV) light, limiting their application in the field of photodetection. In this paper, a heterojunction photodetector (HPD) based on ZnO/CuO/NiO (ZCN) core–shell–shell NWs is reported. The nanoscale copper oxide (CuO) film is deposited on hydrothermally grown ZnO NWs as the visible light absorber. The nanoscale nickel oxide (NiO) shell layer is uniformly coated on the surface of ZnO/CuO NWs by spin coating, which improves the detection capability of the photodetector in the range of UV-to-visible (UV–vis) significantly. Benefited from the large light absorption area provided by the 1D nanostructure and the type II band alignment, the ZCN NW HPD shows a fast response (rise/decay 0.12/0.22 s) and a large sensitivity of 18.65 mA/W under UV irradiation at a 0 V bias. Experimental and simulation results show the key role of NiO shell layer in ZCN NW HPD. Our results suggest core–shell–shell heterojunction nanostructures to develop high-performance photodetectors for next-generation UV–vis broadband photosensing applications.

Temperature Dependence of Electrical Characteristics of ZnO Nanowire Field-Effect Transistors with AZO and Aluminium Source/Drain Contact

In this study, ZnO nanowire field-effect transistor (FET) with an aluminium-doped ZnO (AZO) and an aluminium (Al) dual layer source and drain contact are fabricated and temperature dependent characteristics in the range of 200 – 300 K are analyzed through experimental measurements. The effect of temperature on threshold voltage, subthreshold slope, transconductance, and field effect mobility are analysed. The transfer curve exhibits a parallel shift toward a negative gate voltage direction with a negative shift of the threshold voltage, an increase in the subthreshold slope, and a field-effect mobility as the temperature rises. The electrical properties of the transistors demonstrate typical behaviour at various temperatures.

Influence of Temperature on the Growth of Vertically Aligned ZnO Nanowires in Wet Oxygen Environment

The nanowires (NWs) of zinc oxide (ZnO) are developed effectively on an n-type silicon substrate through a seed zinc (Zn) layer by a wet oxidation technique. The growth is performed at different temperatures, 650, 750, and 850 °C, in a wet and rich oxygen environment under a flow of oxygen in the presence of water vapor at atmospheric pressure with a heating rate of 100 °C in 30 min. At 415 °C, the oxygen gas is introduced for the oxidation process. The Zn seed layer is deposited by the thermal evaporation technique. The structural, morphological, and optical properties are investigated. The temperature effect on NWs of ZnO growth intensity and their direction are explored. The nanowires are grown vertically oriented at a temperature of T = 750 °C. The ultraviolet (UV) analysis has been exposed in the visible region ranging from 10 nm to 700 nm at UV to visible intensity ratio of 2.22. In addition, X-ray diffraction analysis (XRD) is employed to research the structural properties of NWs of ZnO, and the characterization is verified by a scanning electron microscope (SEM) to investigate the morphology.

Free-standing nanowire printed surfaces with high variability in substrate selection for boiling heat transfer enhancement

Nanowires (NWs) constitute a promising solution to the overheating of high-heat-load surfaces in multiphase heat transfer. Typical nanostructure fabrication methods such as complex photolithography and metal-assisted chemical etching (MACE) that utilize patterned templates are limited by high manufacturing costs and type of substrate materials. These limitations significantly hinder the industrial applicability of NW structures in high heat flux units. In this study, we first examine the effect of the morphology of Zinc oxide (ZnO) NW printed substrates, fabricated via microcontact printing (µCP) and solution based growing, on the heat transfer characteristics in pool boiling. Unlike advanced photolithography, µCP offers greater variability and convenience in terms of the substrate selection and large area creation for NW fabrication. Compared with the silicon substrate, the underlying mechanisms for enhancing both the critical heat flux and heat transfer coefficient of ZnO NW substrates are explored by analyzing the surface morphology, bubble, and wicking characteristics of the test surfaces, in order to determine the applicability of boiling heat transfer using ZnO NWs in industrial fields.

Scaling-Up Seeded Hydrothermal Nanowire Synthesis on Non-planar Surfaces Using a Flow Reactor

While many nanomaterial synthesis processes have been demonstrated at the laboratory scale, grand challenges remain at the nanomanufacturing frontier, where it is necessary to maintain tunable material structure and properties at large length scales using high-throughput, low-cost, and sustainable processes. Seeded hydrothermal synthesis is widely used to generate tunable nanostructures with controlled geometric parameters. In this study, we used atomic layer deposition to deposit precise and conformal seed layers which were subsequently processed using a customized hydrothermal flow reactor. The reactor design allows for control of the solution temperature profile in space and time, as well as the solution flow profile. Recirculation of the hydrothermal growth solution enables reduction of the chemical waste by 77–92% compared to a single pass flow reactor. This “surface-directed assembly” process allows for the growth of vertically aligned zinc oxide (ZnO) nanowires (NWs) directly onto macroscopic (cm-scale) non-planar surfaces. We quantify the uniformity of the NW morphology using scanning electron microscopy and UV absorption measurements. The NWs were further functionalized to form superhydrophobic and optically transparent surface coatings along a curved glass dome substrate. The surface coatings were shown to significantly reduce the rate of biofouling from marine algae by ∼75%. This demonstrates a pathway for the scale-up of hydrothermal synthesis processes with a variety of applications in the biological and environmental fields, including medical devices and optical and oceanographic sensors.

Tuning the SERS Capabilities of ZnO Nanowire Arrays Functionalized with Au Quantum Dots for Highly Sensitive Detection of Methylene Blue

AbstractThe development of a surface enhanced Raman scattering (SERS) substrate capable of sensing the target analyte at low concentration has always been demanding. In this prospective, ZnO−Au quantum dots (QDs) hybrid structure with tunable surface properties and high chemical stability is considered a promising material for SERS applications. Here, a novel ZnO@Au QDs hybrid structures with various amounts of Au QDs (ZnO−Aux QDs, where x=0.2, 0.4, 0.6 and 1.0) was synthesized by employing solvothermal along with electrodeposition approach. The optimized substrate, ZnO@Au QDs (0.6) exhibits excellent SERS sensitivity for the detection of MB up to 1 nM with a good reproducibility. The chemical and compositional analysis show that the surface defects are formed due to the interface interactions which not only promote charge transfer between ZnO nanowires and Au QDs complex but also enhanced the Raman scattering of target analyte. The developed substrate demonstrates excellent SERS uniformity which makes them reliable choice for the detection of multi‐analyte for practical applications.

Out-of-Plane Electronics on Flexible Substrates Using Inorganic Nanowires Grown on High-Aspect-Ratio Printed Gold Micropillars.

Out-of-plane or3Delectronics on flexible substrates are an interesting direction that can enable novel solutions such as efficient bioelectricity generation and artificial retina. However, the development of devices with such architectures is limited by the lack of suitable fabrication techniques. Additive manufacturing (AM) can but often fail to provide high-resolution, sub-micrometer 3D architectures. Herein, the optimization of a drop-on-demand (DoD), high-resolution electrohydrodynamic (EHD)-based jet printing method for generating 3D gold (Au) micropillars is reported. Libraries of Au micropillar electrode arrays (MEAs) reaching a maximum height of 196µm and a maximum aspect ratio of 52 are printed. Further, by combining AM with the hydrothermal growth method, a seedless synthesis of zinc oxide (ZnO) nanowires (NWs) on the printed Au MEAs is demonstrated. The developed hybrid approach leads to hierarchical light-sensitive NW-connected networks exhibiting favorable ultraviolet (UV) sensing as demonstrated via fabricating flexible photodetectors (PDs). The 3D PDs exhibit an excellent omnidirectional light-absorption ability and thus, maintain high photocurrents over wide light incidence angles (±90°). Lastly, the PDs are tested under both concave and convex bending at 40mm, showing excellent mechanical flexibility.

A first principles study on spin dependent electronic characteristics of zinc oxide nanowires linked to nickel electrodes

The spin resolved electronic transport behavior of ZnO nanowires (ZnONWs) linked to electrodes is investigated using first principles calculations within Density Functional Theory incorporating the Hubbard (U) term. A defect (resulting from Zn vacancy) in ZnO, as well as the use of Ni electrodes, have a significant influence on the electronic structure properties. They improve the magnetic moment of the system and generate a spin-asymmetric spectra. The ZnONWs linked to the Ni electrodes are probed for spin resolved differential conductance and current. Although the spin down differential conductance curves have a similar trend, the variations in spin up conductance are dissimilar. ZnONW-based devices appear promising for prospective spintronic applications due to their nearly half-metallic behavior around the Fermi energy and acceptable spin polarization in current.

All-in-one supercapacitors with high performance enabled by Mn/Cu doped ZnO and MXene

Here, we report the development of high-performance supercapacitor devices using manganese-doped zinc oxide nanowires (Mn-doped ZnO NWs) and copper-doped zinc oxide nanoparticles (Cu-doped ZnO NPs) as a positive electrode with MXene as a negative electrode. Both transition metal (TM)-based electrodes were used separately with MXene, and the performance was tested. When used in combination with MXene as a second electrode, TM-ZnO samples displayed a major increase in the supercapacitors’ performance. The highest-performance supercapacitor recorded values of 151 F/g specific capacitance along with 84 Wh/kg energy density and a power density of 75 kW/kg. Electron paramagnetic resonance and photoluminescence spectroscopy of Mn/Cu-doped ZnO reveals intrinsic and extrinsic defect signals, which were discussed and attributed to the enhancement of the capacitive performance. The presence of the aforementioned defects optimizes the intrinsic properties and boosts the reaction kinetics, thus providing increased electrochemical activity and superior supercapacitor device performance.

Effects of ZnO nanowire and silica coatings on the inter-yarn friction and ballistic properties of Kevlar fabrics

This paper focused on improving the ballistic performance of plain weave (PW) and twill weave (TW) Kevlar fabrics without affecting the weight. Single layers of fabrics were subjected to two different surface coatings, one with ZnO nanowires (ZnO NW) and other with Silica nanoparticles. Tensile, inter-yarn friction and ballistic properties of bare and surface coated fabrics were evaluated and compared with each other. All types of PW fabrics were found to have superior tensile strain energy, inter-yarn friction and ballistic energy absorption than corresponding TW fabrics. Both ZnO NW and Silica coatings were found to significantly improve the strain energy, inter-yarn friction and ballistic energy absorption of fabrics with only less than 8% increase in the areal density of the fabrics. Among the two surface treatments, Silica coating was found to provide maximum improvement in properties. It increased the strain energy, yarn pull-out energy and ballistic energy absorption in PW fabrics by 67%, 694% and at least 240%, respectively. Also, it increased the strain energy, yarn pull-out energy and ballistic energy absorption in TW fabrics by 42%, 1350% and 387%, respectively. The work demonstrated promising ways of improving the ballistic performance of Kevlar fabrics.

A Zinc Oxide Nanobeam Resonator for Ultrasensitivity Mass Detection

AbstractNanomechanical resonators are expected to be exceptional sensors for high‐performance mass detection, mechanical sensing, and signal processing. In this paper, zinc oxide nanobeam resonators are produced based on single‐crystal ZnO nanowire, which has a typical diameter down to a few nanometers and the length of hundreds of micrometers. This resonator has the characteristics of high aspect ratio nanobeam structure and reliable material. It is observed that the resonance frequency of ZnO nanobeam resonator is up to 1.47 MHz with a high quality factor of 2300 at room temperature, which will play a key role in high‐sensitivity mass detection. The mass detection of ZnO nanobeam resonator is demonstrated by depositing platinum atoms on the middle of the beam, which shows a sensitivity of 11.13 Hz fg−1 indicating its ultrasensitive mass detection capability. In addition, according to the experiment, the molecular dynamics simulations for the resonator is established, which shows that the detection resolution down to 0.2 yg at room temperature can be realized based on this resonator. The results show that the ZnO nanobeam resonator has enormous potential in ultrasensitive detection for biosensing and gas sensing.

On the contact electrification mechanism in semiconductor–semiconductor case by vertical contact-separation triboelectric nanogenerator

With the speed of industrialization accelerating, the traditional energy is in the predicament of being exhausted. Humans urgently need a clean energy to maintain the peace and development. Triboelectric nanogenerator (TENG) is a tiny device that collects and converts the renewable energy, such as wind, vibration and tidal/blue energy, into electrical energy. As the most significant working principle of TENG, contact electrification (CE) has been broadly studied since it was documented thousands of years ago. A large number of related researches are reported. However, most of them are focused on the polymer materials, device structures and potential applications. There are few literatures about the mechanism of CE, especially in the semiconductor–semiconductor case. Semiconductor–semiconductor CE is a promising method to generate electricity, which has been used in many fields, such as the photodetector and displacement sensor. Therefore, it is necessary to establish a serious and detailed theory in order to deeply explain the underlying mechanisms of semiconductor–semiconductor CE. In this work, a novel Fermi level model based on energy band theory is proposed to illustrate the semiconductor–semiconductor CE mechanism. By assembling a ZnO/Si vertical contact-separation (CS) mode TENG, the charge transfer introduced by CE is systematically measured. According to the energy band theory and TENG governing equation, the experimental data is qualitatively and quantitatively analyzed. Moreover, the effects of different concentrations of growth solutions on the morphology of ZnO nanowires and the Fermi level difference between ZnO and Si are explored as well. Results show that it is the Fermi level difference that dominates the short circuit transfer charge amount and direction of semiconductor–semiconductor CE mechanism. Our work can be applied to understand the CE mechanism in semiconductor–semiconductor case and broaden the application prospects of semiconductor-based TENG.

Digitize the Human Body by Backscattering Based Nano-Tattoos: Battery-Free Sensing

Artificial intelligence (AI) lead a new era in remote health monitoring and preventive care, by making wearable electronics, specifically electronic skin, monumental in the future of healthcare. However, remote data collection from these sensors still largely relies on external circuits such as amplifiers, analog to digital converters, and batteries. This extra layer of circuity results in bulky systems, which greatly limits the application of these sensors and forces them to only work at certain places on the human body for limited time, such as only wrist. Here, we present an original technique for producing ink-based nano-tattoos that can be applied anywhere on the human body in various shapes and sizes and transmit data without requiring any external circuit elements, including batteries, by utilizing backscattering communication principles. Ink of nano-tattoos based on ZnO nanowires embedded in graphene aerogels can analyze and track quality of human body movements anywhere there is an ambient wireless signal and a smart phone. This method turns every surface into a potential sensor, digitizing the human body.

Characterization of laser dye concentrations in ZnO nanostructures for optimization of random laser emission performance

Many nanoforms of zinc oxide (ZnO) structures can be synthesized, such as spheres, rods, flowers, disks and walls, as scatter centers in random laser. However, nanoflower and nanowire shapes in this work have received particular interest due to their wide range of applications, including biological, medical cancer cell detection, gas sensors, and biosensors. In this paper, we investigate the optical and morphological properties of two-shaped nanoparticles as scatter centers in the laser active medium on the performance emission of a random laser. Fluorescence and absorption spectra show that 10[Formula: see text][Formula: see text]M for R6G dye and [Formula: see text][Formula: see text]cm[Formula: see text] ZnO NPs are the optimal nanocomposite film concentrations for R6G dye. With excitation energies ranging from 3.44[Formula: see text]mJ to 28.34[Formula: see text]mJ and a repetition rate of 2[Formula: see text]Hz, second-harmonic generation Nd: YAG laser Amplified spontaneous emission (ASE) spectra of the nanocomposite films were observed. The results indicated a minimum bandwidth (Full width at half maximum (FWHM)) of 13[Formula: see text]nm at a threshold energy of 8.65[Formula: see text]mJ for ZnO NW (nanowire) nanocomposite films at [Formula: see text][Formula: see text]cm[Formula: see text] with R6G dye at 10[Formula: see text][Formula: see text]M and Poly(methyl methacrylate) (PMMA). The ZnO NF (nanoflower) nanocomposite film had an FWHM of 11[Formula: see text]nm and a threshold energy of 4.8[Formula: see text]mJ at the same concentrations of R6G dye on PMMA.

A novel flexible and breathable stab-resistance fabric composites with ZnO nanowires growing technology

In this paper, a new flexible stab-resistant composite material was prepared by growing ZnO nanowires on aramid plain fabric by the hydrothermal method. Through SEM, FTIR, and XRD characterization, it is proved that ZnO nanowires have been grown on aramid fabric and the surfaces of aramid filaments become much rougher. Moreover, the inter-filament friction and breaking strength of aramid fabric with nanowires are increased significantly, especially the inter-filament friction, which has been increased by more than 4 times after ZnO nanowires growth. Stab tests were conducted on the bare aramid fabric sample and aramid fabric sample with ZnO nanowires based on the test standard of GA 68–2019. Both of the two samples are 43 layers and are subject to 5 stabs of D1 knife, 3 stabs of D2 knife and 3 stabs of D3 knife. The stab resistance of aramid fabric grown with nanowires is significantly enhanced, and the average penetration depth under the D1 knife impact is decreased by 49.7%. The reason may be that the inter-filament friction increases dramatically with the nanowires and thus the friction energy consumption increases. The flexibility test results show that the softness characteristics of the single aramid fabric and the 43-layer fabric with the nanowires are still maintained. In addition, although the growth of nanowires will lead to smaller voids and a decrease of air permeability of the fabric, the moisture permeability has been slightly improved because ZnO nanowires have the ability to bind with water.

Nanocomposites of ZnO Nanostructures and Reduced Graphene Oxide Nanosheets for NO2 Gas Sensing

A depletion region formed at the junction of two materials depends on the charge carrier concentration and the barrier height. The depletion width can be controlled by the overlayer thickness. Modification of the depletion width after gas exposure is mainly contributing to the sensor response. The maximum effect of gas molecules can be realized when the depletion width becomes comparable to the Debye length. Consequently, the selection of an appropriate overlayer thickness is very crucial. In the present work, chemiresistive gas sensing characteristics of ZnO nanowire (NW) films modified with different thicknesses of reduced graphene oxide (rGO) have been studied. The hybrid films showed selective outstanding NO2 response as compared to pure ZnO NW films. At an optimum rGO thickness of ∼15.3 nm, the response toward NO2 (with a minimum detection limit of 400 ppb) was found to be the highest that is nearly three times higher than that of pure ZnO nanowire films. A synergetic balance of the depletion width at the ZnO/rGO interface with the Debye length is attributed to the improved selective NO2 response of hybrid films.